Recently much progress has been made in the understanding of hair follicle (HF) biology. The HF is a dynamic structure whose multiple compartments undergo successive rounds of complex and highly synchronized architectural reorganization during the growth (anagen), regression (catagen) and resting (telogen) phases of the hair cycle. Several genes that are thought to play a role in the catagen stage of the normal hair cycle, including hairless (hr), the vitamin D receptor (VDR), and the retinoid X receptor alpha (RXRalpha) have been identified on the basis of mutations in these genes which cause hair loss phenotypes. In the case of hr mutations, which cause alopecia in mice and other animals and atrichia with papular lesions (APL, OMIM 209500) in humans, cellular and morphologic changes in the structure of the HF have been characterized, yet little is known about the molecular mechanisms disrupted by hr mutations. Although the function of the protein coded by the hr gene (Hr) remains unknown, several lines of evidence suggest that Hr functions as a transcription factor of the zinc finger type. 1) An Hr domain shares homology with the GATA-1 zinc finger domain, which is responsible for DNA binding. 2) A point mutation in an APL patient results in the substitution of glycine for a conserved, presumably zinc-coordinating cysteine residue at amino acid 622. 3) Hr mutations result in the complete Joss of functional hair follicles, and 4) Hr localizes to the nucleus. This proposal aims to demonstrate that Hr is, in fact, a zinc finger transcription factor by identifying a unique consensus sequence to which Hr binds and by assaying the ability of this sequence to act as a transcriptional regulator or Hairless Responsive Element (HRE). The former aim will be accomplished through random oligonucleotide selection and amplification, a procedure known as CASTing. The latter aim will be accomplished by incorporating any presumed HREs into the promoter of luciferase reporter contructs and assaying transcriptional activity of various constructs in the presence and absence of hairless. Because the hairless phenotype is associated with changes in hair follicle morphology, and one possible mechanism identified is aberrant apoptosis, downstream effectors ofhaMess function might be members of a broad group of cell cycle genes regulated in a tissue-specific manner. The assignment of a role for hairless would be a first step in examining these possibilities.